In the art relating to certain types of internal combustion engines, it is well known to provide pistons having hollow interior portions which are cooled by the delivery of coolant, such as engine oil or other fluid, to the pistons' interior portions. For example, a widely used series of two stroke cycle medium speed heavy duty engines having various applications, among which is the powering of railway diesel locomotives, has utilized for decades hollow piston arrangements cooled by engine lubricating oil delivered through a piston cooling oil system. This system utilizes piston cooling tubes to carry oil from crankcase supported piston cooling oil manifolds into the bottom ends of individual replaceable cylinder liners from which the oil is directed into hollow pistons reciprocably carried in the liners.
The piston cooling tubes, or more specifically the piston cooling oil delivery tube assemblies, used in this system have for many years been made from welded tubes each formed with a U-shaped return bend and having attached thereto a manifold connecting flange and a cylinder liner connecting bracket, the latter being welded to the tube. Each tube includes a portion that extends from the bracket into the liner interior where it turns upwardly into alignment with the cylinder axis. This portion is provided at its end with a nozzle that directs a jet of cooling oil upwardly into an opening, or inlet means, provided in the piston assembly for receiving the cooling oil into a cooling chamber provided in the hollow piston interior.
The just described design of piston cooling tubes was developed to meet not only the requirement of adequate oil delivery and durability but also the necessity for removal of such tubes from the engine whenever the associated cylinder liners piston assemblies are removed for replacement or service. In addition the requirement of reasonable manufacturing cost also required consideration.
Recognizing that the design has provided satisfactory service in commercial operations over a period of many years, it was noted from time to time that certain characteristics of the design or its manufacture resulted in manufacturing and operational problems. For example, the bracket by which the tube assembly is attached to the cylinder liner was formed as a rough forging that required extensive machining in manufacture. Variations in the forging dimensions sometimes caused difficulties in holding the required tolerances, causing additional manufacturing and rework costs. The tube itself was required to be formed by bending in several steps, partly before and partly after the attachment of the bracket by welding. The bending and welding processes were manually accomplished and time consuming, with resulting variations that required the individual alignment of each assembly at installation. In addition, the nozzle was variously formed separately and attached to the tube or formed as a part thereof causing, in either case, certain manufacturing difficulties.
Because of dimensional variations between the mounting location of the piston cooling tube on the oil manifold and that on its respective cylinder liner, caused by manufacturing tolerances and by operational conditions such as temperature variations and possible limited relative motion of the two components, it is necessary that the piston cooling tube be formed with a reasonable degree of flexibility between the manifold and cylinder liner attachment locations. This was accomplished in part by the return bend configuration of the tube and by selection of a tube size and thickness capable of limited flexing and also of maintaining its shape in normal handling and operation. This flexibility, however, resulted in the possibility of bending from rough handling and required that, upon the original installation or reinstallation of a cooling tube in an engine, the nozzle end of the tube be checked with an aiming gauge and adjusted if necessary to obtain the proper alignment of the nozzle opening with the piston cooling inlet so that the oil jet would be properly directed into the cooling oil inlet during engine operation.
Because of these and other problems it was desired to provide an improved design of piston cooling tube which would overcome some of the problems of the previous design and still provide the operational characteristics required.